Process for separating n-monoalkyl and n-dialkyl aromatic amines of the benzene series



Patented Dec. 6, 1932 I EDGAR oi BRITTON AND RAY D. HOLMES, :OEMIDLAND, MICHIGAN, Assrelrons 'i'o THE DOW CHEMICAL COMPANY, OF'MIDLAND; MICHIGAN, A CORPORATIIIONDE -MIOHIGAN PROCESS FOR SEPARATINGL No Drawing. 1 Application filed Apr n13,

As prepared by the usual methods, the alkylated aniline derivatives, such as --d1- methyl aniline, diethyl aniline f di net-hyl p-toluidine, dimethyl p ph'enylene diannne, '5 etc., contain also some Inono-alkylated amhne derivative. These mono-alkylated der1va-" tives although not detrimental in all usages in which the dialkyl anilines ar'e employed' in the arts, are, however; harmful infsomev 1o cases, and must be removed for suchusage. For instance, if mono-methyl aniline be pre ent in dimethyl aniline tothe extent of over 1%, the preparation of nitroso dimethyl aniline therefroni is unsatisfactory due to the presence in the product of N-nitroso methyl aniline; and such raw material. is unsuitable for this purpose unless in some manner purified; Q

Y In our pending application filed September 23, 1927, SerialNo.'221,612, e disclose an improved method orprocess for separating monoand ,di alkyl anilines, whichlcomprisestreating the .mi'xed anilines with an acid anhydride capable of reactingto asubstantial extent with one such anilineonly to form a corresponding acid anil'id, and. sens" .arating the latter from the other anilineflllhe anhydride preferred for use in ,suchqprocess 'is phthalic anhydride, although otheran'hyg 'drides are referred toinsaidapplication as having thecharacteristic;ofthusgreacting preferentiallylwith a mono-alky'l'anil'fne and so adapted for utilization in the manner described and claimed in said application. VV havenow discovered that not gonly will phthalic anhydride serve the desired purpose, but also phthalic acid,'as -Wel1 as certain other acids; which, in other words,- it has been found Will thus reactwith the mono- 0 alkyl aniline in preference to the corresponding di-alkyl aniline. NVe have also discovered that reagents having thecharacteristics in question may belem'ployed to separate de-" rivatives of such mono-anddi-alkyl anilines as Wellas the anilines themselves.

Tothe accomplishment ofthe foregoing and related ends, the invention, then consists of the features hereinafter fully described, and particularly pointed out in the'claims,

e q w e d ri t en. ett na ert i 1192s. semi No} 262 861. a

N-MoNoeLKrL Ann DIALKYL momma; l nin on THEBENZENE snRIns A P tail certain procedure in the application-56f the invention, such "being 'illustrativ"e-, how;- eve rfof but a few of the] various JWay s "in; which theemployed;

Referring by wa 'bf illustration. tdthiuse;

aiiilines to separated, are heated with acid,: aslth'e'result' or which the latter" reacts with ino'noralkyl aniline to: forin mOnofN alkyl-phthalani'lic acid, as tie/represented by the following equation ii l principle ot invention be 5 The resulting acidmay'be readily sep arated from the unreacted di-alkyla'niline in various Ways as'vvellb described more in detail." A small amount of di-Nralkylphih'alanilic'acid may also form, but this compound is easily'separated from the dialkyl aniline by distillation. f i Thesemono-N-alkyl-phthalanilic acids c are generally 'syru py; liquids which are ditficult to obtam in pure forrn, becoming Waxy on cooling. Havinga free carboxyl group present, .theycan, however, be separated from thefdia'lkyl aniline by forming their alkali metal a salts, the following equation illustrating the i reaction Where caustic soda is thus used 4100 :ooora tioned and maybe easily'andcompletely separated y 1 distillation witho ut washing out i the mono-Nralkyl-p'hthalanilic acidfTTh'e; v

di ec ti q d ieis ecb e ate 6f Ten-v faratinglthecompounds in question." Or,'if desired, the di-alkyl aniline may be steam dis-;

'2 acid der-iyative,a pure di-alkyl aniline is "tilled from the phthalic acid derivative. 'As a resultof any of these procedures for separatin'gthedi-alkyl aniline from the phthalic produced. In addition pure monovN-alkyl aniline aswell asrecovering phthalic acid. Where the anhydride. is

.r 'anhydride formfifor reuse, but all of this is i 'used as the reagentin the first described step of the {present process, such anhydride is converted to phthalic ,acid,.-i-n which form it is recovered, i andf'we had previously regarded V Litfas necessary to 'reconvert the acid back to I eliminated'in thepresent'improved process. 7 The'N-alkyl-phthal'anilic acids may be hy- 'drolyzed readilyby'aqueous, acid, or the" alkalizsalt solutionszof the Iphthalanilic acids maybe hydrolyzedbyboiling withexcess" alkali, producing a mono-alkylaniline, which j may be recovered pure, and the phthalic acid which we haye ;now found may be returned directly totthe p roces'sgifor reuse; The following equations will' serve to illustrate the reactions-involved in this stage of the proc ess:'- V

' First, usingalkalisolution:

In; Y

i(mono-bl-alkyl-phthalanllic f acid) -o'ooNa -OOONa I (sadism:

aniline) i .phthalate) 5 7 if (sod iumphthalate) free phthali c'acidy (phthali'c'acid mono-alkyt" aniline hydro sulphate) of these two' methods of hydrolysis ffofthe N alkyl-pththalanic acid may bepracticed as seems advisable and the acid hydrol- 7 I to the above mentioned pro cedures which m'ay be practiced, further treatment of the phthalic acid derivativemay be -car'ried out; for thepurpose of producing Guilt-'NRHiHzSth I similarly beunderstood' that derivative com- As illustrativeexamples showing suitable ysis can becarried out very readily with quite dilute acid, or'desirably with 50'f'per cent.

acids, in addition to phthalic acid, ;have the characteristic of reacting with a mono-alkyl alinine tolform anacid corresponding with 'mono-N-alkyl-phthalanilic acid and so may be utilized in the 'manner' hereinbefore f sulphuric acid at about 100?}Gp11'1 all of the foregoing equations,it willbe understood that IR represents an alkyl group. 1 0 'As hereinbeforeindicated,jotherfcarboxylic 1 set forth-forefiecting the separation of such. mono alkyl'anilinemfrom di-alkyl ani-" line. 'Asexamples ofsuch other acids, suc- 'cinic acid C H .(CO: H)- and maleicv acid, 30 a The x followlng equation corresponding used instead of phthalic acid .v1. *NHR? CECOOH V r 11100011 (niono-tlk yl I (succinic aniline) 7 c i s 'i I 'Nooom OOH From the toregoingdescriptionit will'be rwithlequationl l ri es the reaction with mQno-alkyl anilinewh n acid is thus I r s5 1 v 7 (N-a lkyl-succinanilicacid l:

seen-that the process is, readily adapted for separating 'di-alkyl aniline frommono-"alkylaniline, or vice versa, in order to make either the ,pure mono-- or'di-compound, i. e.,tl1eproc} V ess may be regarded as one for purifying either such compound by removing the other. The process is,'moreover, inexpensiveto carry out and is nevertheless capable of-producing purity than V theseanilinesin a state of greater heretofore attainable.

It will be understood that, as fully setfforth I 1 ,g' 'in'our-pendingapplication Serial NO.221",612,G filedSeptember 23,1927, thel'anhydrides of a the acids named, and I particularly .phthalic ,7

anhydride and succinic'anhydride, react preferentially with the mono-alkyl aniline just i as do-the acidsthemselves', although as here-2'" to'for'e pointed out,.the use of the acid instead of the anhydridesimplifies theprocess and I 'presentsother advantages. Accordingly, the V termdic'arboxylicacidas used in the'following claims should be understood "to connote a dicarb o'xylic' acid capable of reacting with a N-monoalkyl'aromatic amine" of the f a" corresponding. N-dialkyl amine; It -will "benzene series but incapable oireacti'ng with pounds of mono and di-alkyl anilinel-may be separated in accordance with'thepresentim- I 'proved'procedure just ass'uchf a'nilines them I f a 1 100 to 200 C. with 12 grams of phthalic acid. After reaction the dimethyl aniline was distilled off, giving 288 grams of product,

freezing point 22 C. The residue was then treated with the theoretical amount of caustic soda solution and the occluded dimethyl aniline steamdistill d off. The residual solution was then boiled with excess caustic alkali solution-and 3 grams of mono-methyl aniline were recovered. then treated with excess hydrochloric acid (2) 300 grams of dimethyl aniline containing 1.2 per cent. of mono-methyl aniline were heated for four hours at atemperature of 100 to 200 C. with 12 grams of phthalic acid. The reaction product was then treated with the theoretical amount of caustic soda in 10 per cent. solution and the dimethyl aniline was separated and distilled. The sodium phthalanilate solution was treated as above.

The yield of dimethyl aniline was 280 grams, freezing point 2.2. C.

The yield of mono-methyl aniline was. 3 grams.

The recovered hthalic acid was 11 rams.

Other modes of applying the principle of our invention may be employed instead ofthe one explained, change being made as regards the method herein disclosed, provided the step-or steps stated by any of the following claims or the equivalent of such stated step or steps be employed. I

We therefore particularly point out and distinctly claim as our invention:

1. A process for separating N-monoalkyl and N-dialkyl aromatic amines of the benzene series from a mixture thereof, which com-' prises reacting at a temperature between about 100 and about 200 C. the N-monc-v allryl aromatic amine with a dicarboxylic acid and separating the unreacted N-dialkyl, aromatic amine from the reaction mixture.

2. A'pro'cess for separating N-monoalkyl and N-diallryl aromatic amines of the benzene series from a mixture thereof, which comprises reacting at a temperature between about 100 and about 200 C. tllG N-IIIOI10 alkyl aromatic amine with a ,dicarboxylic acid in the absence of a solvent and separatmg the unreacted N-dialkyl aromatic amine from thereaction m1xture.

3. A process for separating N-monalkyl and N -dialkyl aromatic amines of thebenzene series from a mixture thereof, which comprises reacting'at a temperature between about 100 and about 200 C. the N monoalkyl aromatic amine with a dicarboxylic acid in the absence of a solvent, distilling the unreacted N-dialkyl aromatic amine from the This alkaline solution was reaction mixture, hydrolyzingthe'residue from the distillation to liberate free N-1non0- alkyl aromatic amine, and separatingthe lat-- ter from" the hydrolysis mixture.

4. Aprocess for separating N-monoalkyl and N-dialkyl aromatic amines of the benzene seriessfrom a mixture thereof, which comprises reacting the N-monoalkyl aromatic amine with a dlcarboxyhc acid at a temperature between about 100 and about 200 C. in the absence of a solvent, distilling the unreacted N -dialkylvaromatic amine from the re action mixture, hydrolyzing the residue .from the distillation with an aqueous alkaline 'solu tion' and separating the N-monoalkyl aro matic amine from the hydrolysis mixture'v and 11 grams of phthalic acid were recovered.

5. A process for separating N -monoalkyl and Nfdialkyl anilines. from a mixture thereof, which-comprises reacting at 'atemperature between about and about 200 C. the N-monoalkyl aniline with phthalic acid and separating the unreacted N-dialkyl aniline from thelrea'ction mixture.

6. A process for separating N-monoalkyl and N-dialkyl anilines from a mixture thereof, which comprises reacting ata-te1nperature between about 100 and about 200 C. The N-monoalkyl aniline with phthalic acidin the absence of afsolventfand separating the unreacted N -diall'ryl aniline from the reaction mixture.

7 A process for. separating N-monoalkyl and Y-dialkyl anilines from 1 a qinixture thereof, which comprises reacting at a'tenr.

perature between about 100,and about 200 C. the N -monoalkyl aniline with phthalic .acid in the absence of a solvent, distilling the, unreacted N -dialkyl aniline from the reaction mixture, hydrolyzi'ng the residue. from the distillation to liberate free N-monoalkyl anio.

line, and separating thelatter from the hydrolysis mixture.

. 8. A method for separating N-monoalkyl' and N-dialkyl v anilines from a mixture thereof, .which N-m-onoalkyl aniline with phthalic acid-at a temperature between about 100 'and'about 200 C. in the absence of a solvent,.distilling the unreacted N-dialkyl aniline from the re.-

comprises reacting the? action mixture, hydrolyzing the residue from I the distillation with an aqueous alkaline solution, and separating the N-monoalkyl from the hydrolysis mixture.

9. A process for separating N-monomethyl and N-dimethyl anilines from a mixture thereof, which comprises reacting at'a'temj perature between about 100 and-about 200 W Y C. the N-monomethyl aniline with phthalic acid inthe absence of a solvent and separating the unreacted .N-dimeth'yl aniline from the reaction mixture.

11. Aprocess for separating N-monomethyl i and N-dimethyl anilines from amixture thereof, which comprises reacting the N-monorn'ethyl aniline with phthalic acid at a temperature between aboutl00 and about 200 C. in the absence of a solvent, distilling m the unreacted N-dimethyl aniline from the reaction mixture, hydrolyzing the residue from the distillation to liberatefree N-monomethyl aniline, and separating the latter from the hydroly'sismixture. 12; A process for separating N-monoi. ethyl and N-diethyl anilines from. a mixturethereof, which comprises reacting at a temperatur'e'between about 100 and about 200C. the N monoethylaniline with phthal- 21) ie acid and separating the, unreacted N.-di-- V ethyl aniline from the reaction mixture.

13. A process 'for separating Nsmonoethyl and N diethyl anilines fromamixture thereof, which comprises reacting the v 25 N-monoethyl aniline with phthalic acid in the absence of a solvent and separating the unreacted diethylaniline from the reaction mixture. V

14(A process for separating N-monoethyl and N-diethyl anilines from a mixture thereof, which comprises reacting the' N-inonoethyl aniline with phthalic acid at a temperature between100 and 200 C.

I in the absence 'of a solvent, distilling the-un- 5 reacted N-diethyl aniline from they reaction I mixture, hydroly'zing the residue from the distillationto liberate free N-monoethyl aniline, and separating the latter fromthe hy: j jdrolysis' mixture. f a, 4 Q Signed by us, this 10th day of April, 1928.

a EDGAR (lBRITTON;

RAY D. HOLMES, 

